326 research outputs found

    Determinação da aderência entre resinas epoxídicas e argamassas hidráulicas

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    A determina√ß√£o da ader√™ncia entre pol√≠meros e argamassas coloca alguns problemas. A utiliza√ß√£o de ensaios tradicionais como trac√ß√£o directa, flex√£o ou corte, normalmente n√£o permite a determina√ß√£o do valor num√©rico da ader√™ncia. Quando o ligante √© bom e a colagem √© bem executada, a rotura ocorre na argamassa. Este tipo de roturas permite concluir que a ader√™ncia √© superior ao valor da tens√£o de rotura obtida, n√£o sendo poss√≠vel dizer qual o valor num√©rico da ader√™ncia. Utilizando um ensaio baseado na mec√Ęnica da fractura √© mais f√°cil a determina√ß√£o da ader√™ncia. Os provetes com entalhe permitem a concentra√ß√£o de tens√Ķes na junta pol√≠mero/argamassa. Assim, as roturas adesivas s√£o mais frequentes, permitindo a determina√ß√£o do valor num√©rico da ader√™ncia. O provete escolhido para este estudo foi o DCB (‚Äúdouble cantilever beam‚ÄĚ). Os materiais utilizados foram uma resina epox√≠dica e uma argamassa normal. Os ensaios de trac√ß√£o directa das colagens entre estes dois materiais conduziram a roturas na argamassa. No entanto, nos ensaios com provetes DCB obtiveram-se sempre roturas mistas. Para a determina√ß√£o da energia de fractura (Gf) √© necess√°rio conhecer o comprimento da fissura. Este par√Ęmetro altera-se durante o ensaio, n√£o sendo f√°cil a sua determina√ß√£o em cada instante. Para esta determina√ß√£o, utilizaram-se tr√™s m√©todos: emiss√£o ac√ļstica, coloca√ß√£o de um deflect√≥metro no meio do caminho de fissura e complac√™ncia. O m√©todo da complac√™ncia revelou-se mais adequado. Outro problema √© o desvio das fissuras para fora do seu caminho esperado. Para evitar estes desvios, refor√ßaram-se os provetes exteriormente, colando placas de a√ßo. Assim, conseguiu-se que as roturas seguissem o caminho de propaga√ß√£o esperado. Por √ļltimo, para evitar o refor√ßo exterior, utilizaram-se provetes DCB com sec√ß√£o vari√°vel. Estes provetes comportaram-se bem durante os ensaios

    Ader√™ncia entre bet√£o h√ļmido e resinas epox√≠dicas

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    As resinas epox√≠dicas t√™m actualmente muita aplica√ß√£o na repara√ß√£o e na colagem de elementos de bet√£o. A justifica√ß√£o para essa crescente utiliza√ß√£o tem a ver com a excelente ader√™ncia que apresentam nas liga√ß√Ķes bet√£o endurecido-bet√£o endurecido, bet√£o endurecido-bet√£o fresco e bet√£o endurecido-materiais met√°licos. No entanto, a ader√™ncia decresce quando o substrato est√° h√ļmido. A incorpora√ß√£o de uma carga mineral no sistema epox√≠dico permite a obten√ß√£o de uma boa ader√™ncia, mesmo quando o bet√£o est√° h√ļmido no momento da colagem. Neste estudo, a ader√™ncia foi determinada com ensaios de trac√ß√£o directa. Os resultados permitem avaliar a influ√™ncia do tipo, granulometria e quantidade de carga mineral no comportamento de colagens bet√£o endurecido-bet√£o endurecido. A influ√™ncia da espessura da junta foi igualmente avaliada. A apresenta√ß√£o dos resultados efectuase de acordo com um m√©todo de optimiza√ß√£o quadr√°tica que tem em conta a tens√£o e o modo de rotura

    Legislative aspects

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    This chapter contains a lot of information on the new European approach to regulate natural radioactivity in building materials. The main Directive that deals with natural radioactivity in building materials is the Euratom- Basic Safety Standards Directive (EU-BSS) and its approach to regulate building materials is described in Section 4.3. Some additional information on the link with the Construction Products Regulation (CPR) is provided in Section 4.3.1. For the reader who wants to explore the history of the EU-BSS and several important earlier documents in greater depth we refer to Section 4.2. For the reader who wonders how the Euratom drinking water Directive might impact on building materials we refer to Section 4.4. In Sections 4.5 and 4.6 current national legislations on natural radioactivity in building materials are considered in more detail. Several tools are described for the screening of the radiological properties of building materials. These tools are discussed in Section 4.7.info:eu-repo/semantics/publishedVersio

    Key Engineering Materials: Preface

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    Service life of concrete structures rehabilitated with polymers

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    Keynote paperThe estimation of the service life of concrete rehabilitation works is more and more important. The rehabilitation techniques appeared as a need to solve problems posed by the degradation of concrete structures. Some years ago the rehabilitation techniques were not developed and it was important to find solutions for the problems. Now, there is more preoccupation with the service life of concrete rehabilitation techniques, like external strengthening with FRP, increase of concrete sections or reinforcement of cracked sections. The increase of the service life started with the quality of the concrete rehabilitation works. This includes the quality of the design, the products and the execution. Some standards are now available and establish specifications for concrete rehabilitation works. This paper presents the main questions related with this subject. The use of polymers in concrete rehabilitation imposes a different analysis related with durability

    Innovative materials for construction

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    Academic and industrial efforts around the world are continuously engaged to develop new smart materials that can provide efficient alternatives to conventional construction materials and improve the energy-efficiency in buildings or are able to upgrade, repair, and protect existing infrastructures [...]The Guest Editors of this Special Issue would like to thank all the Authors from all over the world (India, Italy, Japan, Korea, Malaysia, Poland, Portugal, Spain), who contributed with their valuable works to the accomplishment of the Special Issue. Special thanks are due to the Reviewers for their constructive comments and thoughtful suggestions. Finally, the Authors are grateful to the Materials Editorial Office, particularly to Jason Huang, for their kind assistance

    Penetrability of chloride ions in concrete protected by an acrylic painting

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    In order do decrease the penetrability of chloride ions in concrete the use of paintings based on polymers can be a good solution. The use of acrylic paintings is recommended because they have good resistance to ultraviolet radiation. It is important to quantify the decrease of chloride ions penetrability obtained by the use of this kind of paintings. The durability of the polymeric paintings is another aspect that needs to be analysed. In this study an acrylic painting was used to protect the concrete and decrease the penetrability of chloride ions. The concrete used was a C12/15, with a cement content of 280 kg/m3 and a water-cement ratio of 0.60. The acrylic painting was applied in concrete specimens 28 days after casting. In order to have a better protection we applied two coats separated by 5 hours. The penetrability of chloride ions was measured following the ASTM standard C 1202 ‚Äď 94. Before the penetrability tests, some specimens were exposed to UV radiation. The exposition to the light occurred by cycles consisting of alternating periods of 8 hours of UV radiation at 60 ¬ļC and 16 hours without UV radiation at 50 ¬ļC. Three kinds of exposition were made consisting on 5, 10 and 15 cycles. The results showed always a high penetrability of chloride ions. This occurred because a poor concrete was used. The protection by an acrylic painting decreases the penetrability of chloride ions. The charge passed decreased about 32 %. However, is not possible to achieve low chloride ions penetrability only with the use of acrylic paintings. It is necessary also the use of a good concrete with low porosity. After the exposition to the UV radiation the penetrability of chlorides ions did not increase. It seems that the UV radiation does not affect the properties of the acrylic painting

    Influência da temperatura no comportamento de elementos de betão armado reforçados à flexão com laminados de CFRP

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    A necessidade de reabilita√ß√£o estrutural de elementos de bet√£o armado tem-se revelado cada vez mais frequente. O refor√ßo por adi√ß√£o de armaduras exteriores atrav√©s da aplica√ß√£o de comp√≥sitos de fibra de carbono √©, actualmente, a t√©cnica de utiliza√ß√£o mais generalizada e com maior potencial. Em muitos casos, a aplica√ß√£o de comp√≥sitos pode significar um meio de aumentar a vida √ļtil de uma estrutura que possivelmente n√£o poderia ser refor√ßada utilizando materiais convencionais. A possibilidade de se proceder √† opera√ß√£o de refor√ßo em per√≠odos de tempo muito curtos, sem que seja necess√°rio interromper, completamente, a utiliza√ß√£o da estrutura, apresenta-se como uma das maiores vantagens associadas ao refor√ßo de elementos de bet√£o armado com materiais comp√≥sitos. A uni√£o entre o refor√ßo e o suporte, geralmente, √© realizada com colas de base epox√≠dica. Contudo, √© nesta parte do sistema que a integridade do refor√ßo pode ser afectada. Entre v√°rios factores, destaca-se a exposi√ß√£o a temperaturas elevadas que pode influenciar a efic√°cia da colagem. Nesta comunica√ß√£o, apresenta-se um estudo experimental, cujos resultados evidenciam que a resist√™ncia t√©rmica deste tipo de sistema de refor√ßo n√£o √© muito elevada

    Assessment of the thermal performance of plastering mortars within controlled test cells

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    Phase Change Materials (PCM) can be incorporated into plastering mortars in order to improve their thermal properties by exploiting latent heat storage of PCMs. As a consequence, plastering mortars that incorporate PCMs can be applied advantageously to building façades/partitions for improved thermal comfort levels while reducing the overall energy consumption for heating/cooling. The assessment of plastering mortars with Phase Change Materials (PCMs) is experimentally investigated in this paper, aiming to assess the effectiveness of the PCM into the mortar, here termed as single PCM plastering mortar (SPCMM). In order to demonstrate the effectiveness of the PCM mortar concept, two experiments have been performed. Two small-scale cubic test cells have been constructed, with outer edge of 26 cm and inner edge of 20 cm. In regard to the outer lining of these two cells, the following applies: one of them was externally lined with conventional mortar (here termed as REFM); and another lined with single PCM plastering mortar. The cells were closed, placed inside climatic chambers and subjected to realistic temperature scenarios in South European countries, whereas the inner temperature was continuously recorded. It was shown that a smoother indoor temperature profile is obtained when PCMs are implemented. An improvement in human comfort can thus be anticipated.Fundação para a Ciência e a Tecnologia (FCT

    Influência de temperaturas elevadas no comportamento de reforços exteriores de betão armado

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    Hoje em dia, h√° a necessidade de resolver problemas em estruturas de bet√£o armado. O refor√ßo por adi√ß√£o de armaduras exteriores √† base de materiais comp√≥sitos √© uma das t√©cnicas que tem vindo a adquirir cada vez mais potencial. A uni√£o entre o refor√ßo e o suporte, geralmente √© realizada com colas de base epox√≠dica. Contudo, √© nesta frac√ß√£o do sistema que a integridade do refor√ßo pode ser afectada. Entre v√°rias raz√Ķes, destaca-se a exposi√ß√£o a temperaturas elevadas. Para estudar a varia√ß√£o do comportamento do sistema de refor√ßo perante o aumento da temperatura ambiente, foram produzidas v√°rias vigas de bet√£o armado onde foram colados laminados CFRP. Ap√≥s exposi√ß√Ķes t√©rmicas c√≠clicas de 25 dias com uma temperatura m√°xima de a 20¬ļC, 40¬ļC, 60¬ļC e 80¬ļC, as vigas foram ensaiadas √† flex√£o. Os resultados demonstram que a melhoria conseguida com o refor√ßo √† temperatura ambiente, se torna menos expressiva com o aumento da temperatura ambiente. A resist√™ncia t√©rmica deste sistema de refor√ßo n√£o √© muito elevada, pelo que a sua aplica√ß√£o em locais quentes, requer cuidados especiais.Nowadays, there is a need to solve problems of reinforced concrete structures. The external reinforcement of concrete with composite materials is a technique that has acquired more and more potential. The bond between the reinforcement and the support is usually accomplished with epoxy adhesives. However, it is in this part that the integrity of the system can be affected, namely by exposure to high temperatures, amongst various other reasons. In order to study the behaviour of the external reinforcement with the increase of air temperature, several beams were prepared and strengthened with bonded CFRP laminates. After cyclical thermal exposure of 25 days with maximum temperatures of 20¬ļC, 40¬ļC, 60¬ļC and 80¬ļC, the beams were subjected to bending tests. The results demonstrate that the improvement achieved with the reinforcement, at air temperature, have no significance with the increase of the environment‚Äôs temperature. The thermal resistance of this strengthened system is not very high, thus special needs are to be taken in to account when applied in warm locations.Sika Portugal, S.A. Socitrel (Soc. Ind. Trefilaria, S.A.). Secil (Companhia Geral de Cal e Cimento, S.A.)
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